Method for producing hydrogenated silicon oxycarbide films having low dielectric constant

ABSTRACT

This invention pertains to a method for producing hydrogenated silicon oxycarbide (H:SiOC) films having low dielectric constant. The method comprises reacting an methyl-containing silane in a controlled oxygen environment using plasma enhanced or ozone assisted chemical vapor deposition to produce the films. The resulting films are useful in the formation of semiconductor devices and have a dielectric constant of 3.6 or less.

This application is a division of application Ser. No. 09/086,811, filedMay 29, 1998, now U.S. Pat. No. 6,159,871.

FIELD OF THE INVENTION

This invention pertains to a method for producing hydrogenated siliconoxycarbide (H:SiOC) films having low dielectric constant. The methodcomprises reacting a methyl-containing silane in a controlled oxygenenvironment using plasma enhanced or ozone assisted chemical vapordeposition to produce the films. The resulting films are useful in theformation of semiconductor devices.

BACKGROUND OF THE INVENTION

The use of chemical vapor deposition (CVD) to produce SiO₂, SiNC or SiCthin films on semiconductor devices from silicon-containing materials iswell known in the art. Chemical vapor deposition processes typicallycomprise introducing the gaseous silicon-containing material and areactive gas into a reaction chamber containing the semiconductorsubstrate. An energy source such as thermal or plasma induces thereaction between the silicon-containing material and reactive gasthereby resulting in the deposition of the thin film of SiO₂, SiNC orSiC on the semiconductor device. Plasma enhanced chemical vapordeposition (PECVD) is typically carried out at low temperatures (<500°C.) thereby making PECVD a suitable means for producing dielectric andpassivation films on semiconductor devices. Silicon-containing materialsinclude silane (SiH₄), tetraethyl orthosilicate (TEOS),silacyclobutanes, and alkylsilanes such as trimethylsilane.

The use of methyl-containing silanes to produce silicon dioxide (SiO₂),amorphous SiNC and silicon carbide (SiC) films by chemical vapordeposition is known in the art. For example, U.S. Pat. No. 5,465,680 toLoboda discloses a method for making crystalline SiC films. The methodcomprises heating the substrate 600° C. to 1000° C. and thereafterexposing the substrate to trimethylsilane in a standard chemical vapordeposition process. EP Patent Application No. 0 774 533 to Lobodadiscloses a method of making SiO₂ coatings from the CVD of a reactivegas mixture comprising an organosilicon material and an oxygen source.EP Patent Application No. 0771 886 to Loboda discloses a method ofmaking SiNC coating from the CVD of a reactive gas mixture comprising anorganosilicon material and a nitrogen source.

As semiconductor device structures become increasingly smaller thedielectric constant as well as the integrity of the film becomeimportant. Films produced by known CVD processes have high dielectricconstants (i.e. 3.8 or greater). Therefore there is a need for processesand materials that result in low dielectric constant films. A newdeposition processes known as Low-k Flowfill®, produces films having adielectric constant of <3.0. This method uses a chemical vapordeposition reaction between methylsilane and hydrogen peroxide toproduce a methyl doped silicon oxide film (See S. McClatchie, K.Beekmann, A. Kiermasz; Low Dielectric Constant Oxide Films DepositedUsing CVD Techniques, 1988 DUMIC Conference Proceedings, 2/98, p.311-318). However, this process requires a non standard CVD system, theuse of a lower stability oxygen source (hydrogen peroxide) and generateswater as a by-product which can be undesirable in semiconductor devices.

It is therefore an object of this invention to provide a method forproducing low dielectric constant thin films of hydrogenated siliconoxycarbide by chemical vapor deposition.

SUMMARY OF THE INVENTION

This invention pertains to a method of producing thin films ofhydrogenated silicon oxycarbide (H:SiOC) having low dielectric constantson substrates, preferably semiconductor devices. The method comprisesthe plasma enhanced or ozone enhanced chemical vapor deposition of areaction mixture comprising an methyl-containing silane and an oxygenproviding gas. By controlling the amount of oxygen available during thereaction/deposition process a film comprising hydrogen, silicon, carbonand oxygen is produced. These films typically have a dielectric constantof 3.6 or less and are particularly suited as interlayer dielectrics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a first semiconductor devicehaving an interlayer dielectric comprising the hydrogenated siliconoxycarbide film of the present invention.

FIG. 2 is a cross-sectional view showing a second semiconductor devicehaving an interlayer dielectric comprising the hydrogenated siliconoxycarbide film of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention pertains to a method for producing hydrogenated siliconoxycarbide films on substrate, preferably semiconductor substrates. Themethod for producing the films comprises the chemical vapor depositionreaction of a reactive gas mixture comprising an alkysilane and anoxygen providing gas wherein the amount of oxygen present during thereaction is controlled. By “semiconductor substrate” it is meant it ismeant to include silicon based devices and gallium arsenide baseddevices intended for use in the manufacture of a semiconductorcomponents including focal plane arrays, opto-electronic devices,photovoltaic cells, optical devices, transistor-like devices, 3-Ddevices, silicon-on-insulator devices, super lattice devices and thelike. Semiconductor substrates include integrated circuits preferably inthe wafer stage having one or more layers of wiring or integratedcircuits before the application of any metal wiring.

The hydrogenated silicon oxycarbide films produced herein may berepresented by the general formula Si_(w)O_(x)C_(y)H_(z) where w has avalue of 10 to 33, preferably 18 to 20 atomic %, x has a value of 1 to66, preferably 18 to 21 atomic percent, y has a value of 1 to 66,preferably 31 to 38 atomic % and z has a value of 0.1 to 60, preferably25 to 32 atomic %; and w+x+y+z=100 atomic %.

The hydrogenated silicon oxycarbide films are produced from a reactivegas mixture comprising an methyl-containing silane and an oxygenproviding gas. Methyl-containing silanes useful herein includemethylsilane (CH₃SiH₃), dimethylsilane ((CH₃)₂SiH₂), trimethylsilane((CH₃)₃SiH) and tetramethylsilane ((CH₃)₄Si), preferablytrimethylsilane.

A controlled amount of oxygen is present in the deposition chamber. Theoxygen may be controlled by the type of oxygen providing gas used, or bythe amount of oxygen providing gas that is used. If too much oxygen ispresent in the deposition chamber a silicon oxide film with astoichiometry close to SiO₂ will be produced and the dielectric constantwill be higher than desired. Oxygen providing gases include, but are notlimited to air, ozone, oxygen, nitrous oxide and nitric oxide,preferably nitrous oxide. The amount of oxygen providing gas istypically less than 5 volume parts oxygen providing gas per volume partof methyl-containing silane, more preferably from 0.1 to 4.5 volumeparts of oxygen providing gas per volume part of methyl-containingsilane. One skilled in the art will be able to readily determine theamount of oxygen providing gas based on the type of oxygen providing gasand the deposition conditions.

Other materials may be present in the reactive gas mixture. For example,carrier gases such as helium or argon, dopants such as phosphine ordiborane, halogens such as fluorine or any other material that providesadditional desirable properties to the film may be present.

The reactive gas mixture is introduced into a deposition chambercontaining a substrate, preferably an semiconductor substrate, whereinthe reaction between the methyl-containing silane and oxygen providinggas is induced resulting in the deposition of a film on the substratewherein the film comprises hydrogen, silicon, carbon and oxygen and hasa dielectric constant of 3.6 or less on the substrate. Any chemicalvapor deposition (CVD) method which has a substrate temperature of lessthan 500° C. may be used herein. Temperatures greater than 500° C. aretypically not suitable for semiconductor substrates, in particularsemiconductor substrates having aluminum wiring. Plasma enhancedchemical vapor deposition (PECVD) is preferred due to the lowtemperatures that can be used and wide use in the industry. Ozoneenhanced CVD may be also be used herein.

In PECVD the gas mixture is reacted by passing it through a plasmafield. The plasmas used in such processes comprise energy derived from avariety of sources such as electric discharges, electromagnetic fieldsin the radio-frequency or microwave range, lasers or particle beams.Generally preferred in the plasma deposition processes is the use ofradio frequency (10 kHz to 10² MHz) or microwave (1.0 to 10 GHz) energyat moderate power densities (0.1 to 5 watts/cm²). The specificfrequency, power and pressure, however are generally tailored to theequipment. Preferably the films are produced using PECVD at a power of20 to 1000 W; a pressure of 1 to 10,000 mTorr; and a temperature of 25to 500° C. Confined, low pressure (1-5 mTorr) microwave frequencyplasmas, often referred to as high density plasmas, can be combined witha RF frequency excitation in a process which helps planarize a varyingsurface topography during CVD growth. This process is useful in theformation of interlayer dielectrics.

The films produced herein may be of varying thicknesses. Films havingthicknesses of 0.01 to 10 μm may be produced by the method of thisinvention. Preferably the films have a thickness of 0.5 to 3.0 μm.

One advantage to the instant method is that when nitrous oxide is usedas the oxygen providing gas, the film composition and properties remainessentially the same even when the amount of nitrous oxide in thereactive gas mixture is significantly varied (1.2:1 to 4.5:1 volumeparts N₂O to methyl-containing silane)

Another advantage to the method of this invention is the ability to linksuccessive growth processes to produce multilayer structures for exampleof SiO₂/H:SiOC/SiO₂ or SiC:H/H:SiOC/SiC:H by increasing or deleting theoxygen providing gas at the appropriate time during the CVD process. Itis preferred to produce discreet layers by stopping the reactive gasflow, adjusting the amount of oxygen providing gas and thereafterresuming the reactive gas flow to produce the next layer.

The films produced herein, due to the low dielectric constant, areparticularly suited as interlayer dielectrics in semiconductorintegrated circuit manufacturing including, but not limited to, gatedielectrics, premetal and intermetal dielectrics and passivationcoatings. The films produced herein have a dielectric constant of 3.6 orless, preferably, 3.2 or less, more preferably 3.0 or less.

FIG. 1 shows the film produced herein as intermetal dielectric on afirst semiconductor device. As seen in this figure, there is asemiconductor substrate 10 having a wiring layer 11 covered by ahydrogenated silicon oxycarbide film 12. FIG. 2 shows the film producedherein as an intermetal dielectric on a second semiconductor substrate.As seen in this figure, there is a semiconductor substrate 20 withmultiple wiring layer 21 and multiple layers of hydrogenated siliconoxycarbide films 22.

EXAMPLES

So that those skilled in the art can understand and appreciate theinvention taught herein, the following examples are presented, it beingunderstood that these examples should not be used to limit the scope ofthis invention found in the claims.

In Examples 1-9 and Comparative Examples 1-2, dielectric properties weremeasured using metal-insulator-semiconductor (Examples 4-9) andmetal-insulator-metal capacitors (Examples 1-3, Comparative Examples1-2). Measurements were performed immediately after the metal gatedeposition (top electrode) and again after one or more anneal cycles inN₂ in the temperature range of 350 to 400° C. Relative permittivity, K,was calculated from the capacitor geometry and the film thickness.

Examples 1-9

A reactive gas mixture comprising trimethylsilane (3MS) and nitrousoxide (See Tables 1 and 2 for gas flow amounts) was introduced into acapacitively coupled parallel plate CVD system using thermally oxidized(0.1 μm SiO₂) silicon wafers coated with 0.5 μm Al or bare siliconwafers as the substrates. The PECVD system was operated at a power 350W, pressure of 2700 mTorr and temperature of 250° C. Helium was used asa carrier gas. The dielectric constant, growth rate and film stress(compressive) results for Examples 1-9 are in Tables 1 and 2. Thecomposition and density of the films produced in Examples 4-9 are inTable 3. As can be seen in Table 2, even when the amount of nitrousoxide is significantly varied, the resulting films have essentially thesame composition and properties.

TABLE 1 Example 3MS He N₂O K K (400° C. post Rate Stress* No. (sccm)(sccm) (sccm) (MIM) metal anneal) (Å/min) (MPa) 1 100 380 120 3.6 3.6535 61 C 2 100 260 240 3.4 3.1 to 1531 28 C 3.4 3 100 140 360 3.22.8-3.0 3615 53 C * C = compressive stress

TABLE 2 K Growth Example 3MS He N₂O K (post metal Rate No. (sccm) (sccm)(sccm) (MIS) anneal*) (Å/min) 4 100 380 120 3.2 3.1 624 5 100 260 2403.1 3.0 2076 6 100 140 360 3.1 3.1 4830 7 100 100 400 3.0 2.9 5510 8 10050 450 3.1 3.0 6076 *three cycles, one hour soak each, 200-350-200° C.,200-400-200° C., 200-400-200° C.

TABLE 3 Example Thickness Si H C O Density No. (μm) atom % atom % atom %atom % g/cc 4 0.62 0.20 0.25 0.37 0.18 1.46 5 0.83 0.18 0.29 0.35 0.181.34 6 0.97 0.2 0.3 0.31 0.19 1.36 7 1.10 0.18 0.29 0.33 0.20 1.36 81.22 0.18 0.27 0.34 0.21 1.36

Comparative Examples 1-2

Using the same procedure for Examples 1-8, a reactive gas mixturecomprising trimethylsilane and oxygen were used in the plasma enhancedchemical vapor deposition. Results are given in Table 4. The resultingfilms were essentially SiO₂ films due to too high of an amount of oxygenused in the reactive gas mixture.

TABLE 4 Growth Example 3MS He O₂ K K (400° C. post Rate Stress* No.(sccm) (sccm) (sccm) (MIM) metal anneal) (Å/min) (MPa) C1 100 440  604.6 — 1456 60 T C2 100 380 120 5.8 — 2481 71 T * T = tensile stress

Comparative Example 3

This example is Example 3 of EP Patent Application No. 0 774 533 A1. Areactive gas mixture comprising 6 sccm of trimethylsilane (TMS) and 523sccm of nitrous oxide was introduced into a capacitively coupledparallel plate PECVD system using silicon wafers as the substrates. ThePECVD system was operated at a power of 50 W, a pressure of 1000 mTorrand a temperature of 300° C. Helium (500 sccm) was used as a carriergas. Due to the high amount of nitrous oxide (N₂O) being used, theresulting film was a SiO₂ film.

What is claimed is:
 1. A semiconductor device having thereon a filmproduced by introducing a reactive gas mixture comprising amethyl-containing silane and an oxygen providing gas into a depositionchamber containing a semiconductor device and inducing a reactionbetween the methyl-containing silane and oxygen providing gas at atemperature of in the range of 25° C. to 500° C.; wherein there is acontrolled amount of oxygen present during the reaction to provide afilm comprising hydrogen, silicon, carbon and oxygen having a dielectricconstant of 3.6 or less on the semiconductor device.
 2. Thesemiconductor device as claimed in claim 1 wherein the film has aformula of Si_(w)O_(x)C_(y)H_(z) where w has a value of 18 to 20 atomic%, x has a value of 18 to 21 atomic percent, y has a value of 31 to 38atomic % and z has a value of 25 to 32 atomic %; and w+x+y+z=100 atomic% and the film has a thickness of 0.01 to 10 μm.
 3. The semiconductordevice as claimed in claim 1, wherein the methyl-containing silane isselected from the group consisting of methylsilane, dimethylsilane,trimethylsilane, and tetramethylsilane.
 4. The semiconductor device asclaimed in claim 3 wherein the methyl-containing silane istrimethylsilane.
 5. The semiconductor device as claimed in claim 1wherein the oxygen providing gas is selected from the group consistingof air, ozone, oxygen, nitrous oxide and nitric oxide.
 6. Thesemiconductor device as claimed in claim 1 wherein the oxygen providinggas is nitrous oxide.
 7. The semiconductor device as claimed in claim 1wherein the methyl-containing silane is trimethylsilane and the oxygenproviding gas is nitrous oxide.
 8. The semiconductor device as claimedin claim 1 wherein the amount of oxygen providing gas is less than 5volume parts oxygen providing gas per volume part of methyl-containingsilane.
 9. The semiconductor device as claimed in claim 1 wherein theamount of oxygen providing gas is 0.1 to 4.5 volume parts of oxygenproviding gas per volume part of methyl-containing silane.
 10. Thesemiconductor device as claimed in claim 1 wherein the reaction isinduced by exposing the reactive gas mixture to plasma.
 11. Thesemiconductor device as claimed in claim 1 wherein the film has adielectric constant of 3.2 or less.
 12. The semiconductor device asclaimed in claim 1 wherein the film has a dielectric constant of 3.0 orless.
 13. The semiconductor device as claimed in claim 1 wherein thehydrogenated silicon oxycarbide film has a thickness of 0.01 to 10 μm.14. The semiconductor device as claimed in claim 1 wherein thehydrogenated silicon oxycarbide film has a thickness of 0.5 to 3.0 μm.15. A semiconductor device having thereon a film has a formula ofSi_(w)O_(x)C_(y)H_(z) where w has a value of 18 to 20 atomic %, x has avalue of 18 to 1 atomic percent, y has a value of 31 to 38 atomic % andz has a value of 25 to 32 atomic %; and w+x+y+z=100 atomic % and thefilm has a thickness of 0.01 to 10 μm.
 16. The semiconductor device asclaimed in claim 1 wherein the semiconductor device is an integratedcircuit in a wafer stage having one or more layers of metal wiring. 17.The semiconductor device as claimed in claim 1 wherein the semiconductordevice is an integrated circuit in a wafer stage before any applicationof metal wiring.